The field of the invention is integrated circuit packaging.
High density electronic interconnections are required for many important applications including ball grid array packages, high density electronic circuit boards, cell phones and other miniature electronic devices. In one fabrication scheme for high density interconnection, electronic circuitry is fabricated onto both sides of individual layer pairs with through vias connecting the circuitry on the two sides, These layer pairs may then be physically and electronically joined by fabricating a bond ply material with through-holes drilled or lased, filling these holes with sinterable conductive pastes or solders, by stacking the layer pairs and the bond plies in a press, and by curing the resulting structure. The curing process can sinter the paste or solder providing for electronic interconnection between layer pairs and at the same time cure the bond ply material, providing for permanent physical bonding of the structure. However conductive inks and pastes and solders generally shrink significantly during the sintering or soldering process. This shrinkage occurs as the solder or paste sinters, often causing voids or open circuit interconnection. The shrinkage also can force considerable stress into the overall structure, leading to unreliable interconnection or bonding between the layers. Thus, there is a need for material and associated processes which can compensate for this shrinkage providing for stress-free and reliable electronic interconnection between the layer pairs.
The present invention is directed to a unique bond-ply structure and associated processes for processing of the bond-ply structure and for joining together circuit layer pairs. The disclosed structure and methods makes it possible to create a bond-ply having raised structures of conductive material which compensate for shrinkage during sintering, thus creating a stress-free and void-free electrically conductive junction between layer-pairs in an interconnect.
Various objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the invention, along with the accompanying drawings in which like numerals represent like components.